No difference. An AR pistol receiver is the same receiver used on a rifle (most of the time, there are a few oddballs out there, very uncommon).
By adding a shoulder stock to a pistol you are creating a SBR. Just like if you put one of those stock things on a Glock, adding the rec ext and stock to the AR pistol you have now made a rifle.

Joat

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2. You would like to get a second upper and put a SBR 9mm Carbine together too.

If my guess is RIGHT, You WILL need a new tube with a stock +/- spring. Additionally, you *may* need a second buffer +/- buffer spring for the 9mm. You may need a "hookless" hammer for the 9mm as well.

The AR pistol length gas systems put a lot of pressure into the gas tube and therefore push on the bolt carrier group rather violently. They use a pretty heavy buffer to combat the elevated pressures from the short gas tube.

The AR 9mm uppers are blow back. They may work with the heavy buffer and spring, but may not. Be sure that your hammer is correct for the bolt on the 9mm upper. If they are RAMPED BOLT CARRIERS, then you can still use the "traditional" AR hammer. If it is NOT ramped, then you need the 9mm hammer without the "hook" on it. The hook will cause "early cocking" of the hammer as well as put a lot of stress on the hammer pin at least. In the worst case, it can bind up between the bolt carrier and hammer, and that can be a BIG headache. (When the bolt is bound up partially open you can't remove the upper from the lower.)

EDIT: The need to intechage all these parts each time I want to switch calibers really pushed me towards a dedicated 9mm Carbine build. FWIW.

Though the DPMS hammers will work on the Colt/RRA type 9mm uppers, I'd recommend swapping a 9mm hammer in with the 9mm buffer when using the 9mm upper.

Also, don't forget to get your lower engraved before you get your approved form 4 back. Remember to register it on the F4 as both 9mm and 223 or you'll need to send a letter of intent to the NFA branch to update your NFA status.

Don

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Remember to register it on the F4 as both 9mm and 223 or you'll need to send a letter of intent to the NFA branch to update your NFA status.

sorry to hijack your thread but quick question...exactly how many calibers can you put on a form 4 for 1 SBR?

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Multi calibers is OK from what I've heard. On my personal SBR's , they were F4 as .223 and I send a letter of intent to utilize different barrel lengths and calibers in a letter to the NFA branch requesting that they update the status of the NFA firearm in question. Once they acknowledge receipt of the letter, any config you advised them of is good to go.

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Remember to register it on the F4 as both 9mm and 223 or you'll need to send a letter of intent to the NFA branch to update your NFA status.

Quote:

Multi calibers is OK from what I've heard.

You never know what is going to slip through different examiners at the NFA branch but “Multi” and a range of lengths are not ok anymore. You can list additional calibers in 4h of the form 1, you should just have the upper described on the f1 handy at all times.
You'll just waist time turning in something wrong so just give them a call at 304-616-4500 with your questions.

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